Loud speaker



`I'uly 11, 1933. B. A. ENGHOLM LOUD SPEAKER original Filed May so., 1930 "F1436 m3 7301i M+ Ulm,

y Patented July 11, 1933 UNITED sTATEs PATENT OFFICE BERNARD A. ENGHOLM, OF LAKEWOOD, OHIO, ASSIGNOR TO TI-IE ROLA COM-PANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO LOUD SPEAKER Original application led May 30, 1930, Serial No. 457,552. Divided and this application filed August 12,

1932. Seriall This invention relates to electrodynamic loud speakers, and particularly to the voice coil form, which embodies partof the structure thereof. The present application is a division of my prior application, Serial No. 457,552, filed May 30th, 1930.

One form of loud speaker which is in general use utilizes a tympanum in the form of a cone with a moving coil mounted adjacent the apex end thereof. Considerable difficulty has been experienced in making a coil form, which Would have sufficient strength to withstand the necessary handling, incident -to the asselnbling operations, and which at the same time would be sufliciently light in weight to keep the mass and moment of inertia at a minimum.

One coil form hereto-fore used has embodied a heavy paper cylinder on which the coil has vbeen Wound. To provide sufficient strength to permit attachment of the form to the con-e and supporting spider, however, it has been necessary to reinforce the forni with an additional layer or collar of paper. The form projected beyond the end of the collar and had to be glued onto the inner face of the cone. Thisform of construction is objectionable, for it has been difficult to prevent the end turns of the coil from slipping off the form during the Winding and subsequent handlingr operations. Furthermore, the use of an additional supporting collar increases the number of manufacturing operations while the connection between the forni and cone has necessitated a delay in the assembling operation, until an adequate period of time has elapsed for the glue to dry.

Another form, which has been used, comprises a cylindrical member of rigid material` which is nearly equal in thickness tothe depth lof the Winding. The member is then turned down oni a lathe to form a. peripheral groove in which the coil may be wound. This obviously is an expensive procedure and is objectionable, as it does not overcome. the difiiculty of providing satisfactory means for connecting the forni vto the cone.

An object of the present invention, therefore` is to make a voice coil form that will be extremely light in weighty and yet have the desired rigidity to hold the coil in proper position.

A further object is to provide a` form which can readily be made to assume the desired cylindrical form With a high degree of ac-A curacy, and which will maintain such shape for an indefinite period during operation.

Referring now to the drawing, Fig. 1 is a vertical section taken through a loud speaker assembly, embodying my invention; Fig. 2 is a plan View of a blank from which a voice coil form may be made; Fig. 3 is a section through a forming mold with the blank positioned therein; Fig. 1 is a perspective vie-W showing the shape of the form at the completion of the forming operation; Fig. 5is a perspective view showing the voice coil assembly on the form; Fig. 6 is an end view of the coil form attached to the supporting spider. and Fig. 7 is a perspective view of one of the collars. which may be used for connecting the coil form to the spider.

The invention is shown in connection with a loud speaker of the cone type, having a dia-- .phragrn or tympanum 10, which is preferably frustro-conical in shape, and which may be fastened at the base thereof to a collar 11. which in turn is fianged at l2, and is adapted to be fastened between the flange of a housing 13 and a clamping ring 14. The housing may carry a spider 15, which supports the diaphragm adjacent the apex end thereof. To this end, the diaphragm is shown as being fitted between a collar 16 and a voice coil form, as indicated in general at 17. The housing 13 in turn may be mounted on a field coil structure, which comprises a shell 20 that has a central core 21, carried thereby, and a face plate 22, which is positioned between the shell and the housing and which coacts with the core to provide an air gap Within which" the voice coil 23 is positioned. The field coil 24 surrounds the core and is disposed within the shell.

The present invention relates more particularly to the'structure of the voice coil form and contemplates the provision of a form which is extremely light in Weight and yet which has sufficient rigidity to obtain the desired cylindrical form and to hold the voice of the form, and

coil thereon. The form may be made in various ways, but the preferred'arrangement includes the steps of cutting a strip of material 19, such as paper, having a thickness of from four to eight thousandths of an inch and having a length equal to the circumference of the form. The strip is then bent into the shape of a cylinder with the ends in abutting engagement, and is placed in a cylindrical mold 25. To facilitate accurate alignment of the ends of the strip when bent to cylindrical4 form, I provide a small tab 26 on one end and a corresponding notch 27 on the other end. Thus, when the strip is bent into cylindrical shape, the tab iits into or meshes with the notch. Furthermore, when the blank 19 is initially made, I provide pairs of openings 28 and 29, as is shown in Fig. 2. The openings 28 are in one longitudinally extending row and those indicated at 29 are in a parallel row.

ese openings are utilizable for holding the ends of the wire in position during and after the winding operation.

It is desirable that the coil 23 be disposed between the shoulders on the form. To this end, the form may be bent to provide the desired shoulders by pressing it outwardly against the walls of the die. Accordingly, the mold 25 is shown as having an annular groove 30, formed on the inner surface and spaced above the bottom thereof. A second groove 31 may then be disposed below the groove 30 and adjacent the region occupied by the lower edge of the blank. The blank is then forced outwardly into the grooves by means of a plunger 32, which has a head 33 of soft rubber and which operates when forced into the mold through the form to stretch the f paper and cause it to assume the contour of the mold. This, therefore, provides one shoulder in the form of a bead 35 at one end a rib 36 between the ends of the form. The space between the rib and bead then constitutes a groove 37, into which the coil 23 may be wound. The bead and adjacent end of the rib, therefore, act as limiting shoulders to assist in keeping the coil in place on the form. Furthermore, the position of the rib forming groove 30 in the mold is such that the openings 28 are disposed at one end of the rib,wl1ile the openings 30 are disposed at the other end of the rib. Thus. When the ends of the coil are passed through an opening 29 and then through an opening 28, the wire lies within the hollow of the rib and is thus in alignment with the inner surface of the coil form.

The openings through which the wires eX- tend has thus important manufacturing advantages. For example, one end of the wire may be quickly threaded throl'igh one pair of openings and then bent backwardly upon itself, It can thus be satisfactorily held against movement during the winding operation without requiring it to be looped or twisted around any member. When the windlng operation is completed, the opposite vend may be threaded through the remaining pair of openings. During the winding operation cement is used for securing the coil turns in place. The openings, therefore, serve as a means of bringing out the leads and at the same time holding the coil in proper posisition until the cement is dry.

To provide an expeditious manner of connecting the coil form to the cone, I fasten a light metallic ring 40 onto the spider, adjacent the inner wall 41 thereof, and I cover the end portion 42 of the form with cement or glue, and insert it into the ring 40. The apex end of the cone 10 is split for a distance about one-eighth of an inch to form segments or tabs, and these are then bent until they extend parallel to the axis of the cone.l They'are then inserted into the end of the form and are glued or cemented thereto. To hold the tabs firmly against the form, I may use the metallic ring 16, which is slightly in excess of the inside diameter of the cone tabs. The ring has a conical ex- -tension 45, which is tapered in conformity with the cone. After the surface of the ring is glued or cemented, it is then pressed against the tabs, thus forcing them outwardly against the voice coil form, and in turn forcing the form against the ring 40. Thus, the entire assembly is securely locked together. I

While I have illustrated and described one method of making the coil form, it is to be understood that other methods are within the scope of my invention. For instance, the orm may be cut initially from a paper cylinder, the cylinder dropped into the mold, and then pressed outwardly and stretched until it conforms to the desired shape.

An important advantage of a voice coil form which is made in accordance with my invention is the fact that the material is stretchable and that it has a uniform thickness throughout. Thus, I obtain a strong yet light form, which makes the voice coil more sensitive to current fluctuations and therefore more efficient in sound reproduction than any of the heavier coil forms heretofore known. Furthermore, by following the preferred method of making the article. I obtain a die-formed structure, which can be accurately made, and which will maintain its shape for a long period of time.

claim:

1. A voice coil form, having spaced openings arranged in pairs, each pair cooperating to provide a passageway on the inner side of the form for carrying the leads of a voice coil into and out of the form.

2. A cylindrical voice coil form of substanti ally uniform thickness throughout, said form having a coil'receiving portion at one end thereof and having a diaphragm engaging portion adjacent the other end thereof, and a raised portion therebetween, the raised portion providing passageways through which the leads of a coil on the form may be passed.

3. A voice coil form comprising a substantially tubular member, having a coil positionlng abutment thereon, said form being provided with a Wire receiving perforation adjacent the abutment, and having substantially uniform thickness throughout.

4. A voice coil form comprising a single strip of material having spaced shoulders defining a coil receiving groove, and having wire receiving perforations therein adjacent one end of the groove, the material of the form being of substantially uniform thickness throughout.

5. A form comprising a single strip of material having a bead formed therein adj acent one end thereof, and having a shoulder formed therein intermediate the ends thereof, the shoulder and bead having the same thickness, as the remaining part of the form and cooperating to provide a coil receiving groove.

6. A coil comprising a substantially cylindrical member of uniform thickness throug out and having spaced shoulders to provide coil receiving groove, and valso having a Wire receiving perforation therethrough adjacent one end of the groove.

lindrical member, having means defining a I coil positioning abutment including a shoulder upset from the material of the form, and having a perforation adjacent the shoulder extending from the outer to the inner face of the form, the shoulder providing a cavity on the face of the form to receive said terminal lead.

9. A form comprising a substantially cylindrical tubular member having a recess on the inner face thereof, and having an aperture adjacent the recess for providin a passagevvay through ythe form for the ead of a coil positioned on the form.

n testimony whereof, I hereunto aiX my signature.

BERNARD A. ENGl-TOLM- 

